Fluorescent color screen for electron optical systems



prll 3, 1951 E. G. RAMBERG 2,547,775y r FLUORESCENT coLoR SCREEN FORELECTRON OPTICAL SYSTEMS Filed Jan. 25, 1946 YEZOW BLUE P//SFWRPHOJP//OR CONTROL W INVENTOR www ATTORNEY Patented Apr. 3, 1951 UNITEDySTA'IES PATENT OFFICE FLUORESCENT. COLOR SCREEN FOR ELECTRON: OPTICALSYSTEMS Edward' G. Ramber'g,

to Radio Corporatio tion offDelaware Feasterville, Pa., assignor n ofAmerica, a corpora- ApplicationJanuary 23, 1946,A Serial No.7642,950

3` Claims; (Cl. 2'50-164) 7 The'instant invention is related to.applicants", copending application -Serial No. 642,949, filed) January23, 1946,' andV issued June 8, 1948, as

Patent No. 2,442,961, which discloses a colorv photographic plate whichresponds selectively to' impinging electrons of different electron'velocity.

The instant invention also is related to the Sys'j tem disclosed andclaimed in U1 S. Patent".v

2,372,170, granted. to Richardv` F. Bakerv onv MarchKV 77 thatphotosensitive materialsv respond. with.'

the specimen or of variations in the thickness of.

thev specimen. The constant velocity electrony beam derivecl'from theelectron gun of a conventional cathode ray oscilloscope or televisionkinescope also may be varied in velocity by uctuator variable potentialsapplied to a control electrode operative lupon the electron beam.

The instant invention contemplates the use of a multicolor uorescentscreen for use in anelectron microscope or cathode ray oscillographicdevice for recording4 the diierences in the velocity ofi electronsimpinging thereon. in' terms of thev color or colors of the screenfluorescence.

l Thefcolor selectivey electron responsive uorescentscreen accordingl tothe invention may comprise, for example, two or more parallel layers ofdiierent fluorescentmaterials which provide dif-V ferent color lightemission. Forexample, athin layer, of willemite or cadmium-zinc,sull-ide which'.

provides yellow light emission may be superposedl upon a, layer ofzinc-sulfide which provides blue light emission in response to electronbombardment..

" I'f the. thickness of the yellow light emissive.

layer is selected tocqual approximately the pene-- tration thickness ofthe slowest electrons impinging on the screen, these electrons willAprovide yellow light emission. Somewhat-,faster elec-` tronswill alsoexcite the, lower blue light emissive uorescent layer, thereby providinga combination of both yellow and blue. emission with a re,- sultantgreen color. Very fast electrons Willexcite the blue emissive layer tova greater extent.

than the yellow emissive layer, thereby providing.

substantially only a bluelight. In order to obtain wide color diierencesfor relatively small differences in electronvelocity, the. top oryellow.v light emissive layer. may beselected. to have greatestefficiency toV electrons within predetermined velocity ranges.

j Among the objects of the invention are to'proi-4 vide an improvedmethodof vand meansn for measuring; electron` velocities. Ajnother'object is tof, provide an improved method ci" and means forjestablishing selective uorescence in response toKV electron bombardmentby' electrons of dilierentf velocities. Anl additional' object is toprovid'ej means for producing selective`- color fluorescence of` a@fluorescent screen in electronV optical'V apr, paratus in response tothe impingement thereon7 fv electrons having differentelectronvelocitie'si-'L A further object is to` provide an improvedlcolorfuorescent screenproviding dilerentcolor'iiuo rescence in responsetova'riations of the velocity-f ofelectrons' i'mpingin'gxA thereon. Astill further object of the invention is to provide anE improved'color-selectiveA uorescent screen for electrony microscopes; cathoderayl` voscill'oscopesv and? telev-i'sion kinescopes comprisingjuxtaposed layer's of diierent fluorescent materials providing dif-1ferent color light' emission in response to'- differentvelocity electronbombardment, Anotherobiect" isltovprovide an'improved method of andmeans; for varying thecolor sensitivity; of amultilayer,t multicolorfluorescent" screen in'v response' toi bombardingfv electronsv havingdiiierent electron velocities. l The invention: will bev described! in,further. de:-y tail` by reference to: the.` accompanying drawingl offwhich Figure. 1 is a schematic diagram of a', typical electron,microscope1 employing a multi'- color uorescent screen-f. according; tothe-invention, Figure `v2v isv afamilyof graphs illustrating; theselective .colorv lightemissive-properties-of tWof phosphore whichl maybe, eniployeol to provide al multicolor uorescent screenvv according to.the. invention, ,and` Figure 3` islal schematic diagram of a cathode.ray o scilloscopeV or similar oscillolower light emission efficiencythanthe bottom orv blue. light emissivelayer,

graphic device employing a multicolor fluorescent screen according tothe invention. Similar refl" erence, characters are applied tosimilar'elements throughout the drawing. v

1945, which discloses and utilizes the fact' Referring to Figure 1 ofthe drawing, the invention is illustrated in combination with aconventional electron microscope. The system includes an electron sourceI which is focused upon a microspecimen 3 by an electrostatic orelectromagnetic condenser lens 5. Electrons transmitted by themicrospecimen 3 are focused by an objective lens I and projection lens 9to provide a greatly magnified electronic image at the plane of afluorescent screen II. The fluorescent screen comprises a support I3upon which is deposited an under fluorescent layer I5 comprising, forexample, zinc sulfide which provides blue light emission in response toelectron bombardment. A second, or outer, fluorescent layer I'I ofwillemite or cadmium-zinc sulfide is deposited over the rst zinc sulfidelayer I5 and provides yellow light emission in response to electronbombardment. It should be understood that any other combination of knownfluorescent phosphors may be employed to provide the desired multicolorfluorescence in response to electron bombardment of predeterminedelectron velocities.

The thickness of the outer phosphor layer II should be selected to equalapproximately the penetration thickness for the slowest electronslimpinging upon the screen. Such minimum velocity electrons thereforewill produce yellow light emission from the outer phosphor layer II.Somewhat faster traveling electrons will excite the under phosphor layerI5 as well, providing blue light emission therefrom which, when combinedwith the yellow light emission from the outer layer II, will provide agreenish luminescence. Much faster traveding electrons bombarding thescreen will excite the under phosphor layer I5 to a greater extent thanthe outer phosphor layer II, thereby providing substantially blueluminescence.

If it is desired to obtain high color differentiation for relativelysmall differences in electron velocity, the material of the outerphosphor layer I'I should be chosen to be less eicient than that of theunder phosphor layer I5. In the example illustrated,50 kilovoltelectrons will provide greatest excitation of the outer prosphor layerII, thus producing yellow luminescence thereof, and 70 kilovoltelectrons will provide greatest excitation of the under phosphor i layerI5, thus producing blue luminescence thereof. Electrons havingvelocities in the range between 50 and 70 kilovolts will produce varyingshades of greenish luminescence. Thus, if the velocity of the electronicimage derived from the microspecimen 3 is controlled in any known mannerwithin a desired velocity range, high color contrast will be provided bythe multicolor screen. The contrasting colors of the electronic imageprovided bythe screen may be interpreted in terms of variations inthickness or composition of the portion of the microspecimen imaged uponthe screen.`

It should be understood that any desired number, greater than one, ofcontrasting color phosphors may be employed to extend the observablevelocity range of the electrons comprising the electronic image, andthat varying thicknesses of the several phosphor layers may be employedto determine the desired color contrast and sensltivity.

Figure 2 shows a pair of graphs I9, 2I, illustrating, respectively, themagnitudes of fluorescence of the screens I1 and I5, respectively, as afunction of the velocity of the electronic image exciting said screens.

Figure 3 illustrates the use of a multicolor screen in accordance Withthe invention in combination with a cathode ray oscilloscope ortelevision kinescope 23. The oscilloscope includes a heater element 25for producing electronic emission from an indirectly-heated cathode 2'I.An anode 29, biased to a high positive potential with respect to thecathode, accelerates the electrons derived Afrom the cathode 21 andfocuses them to a ne cathode ray which is deflected laterally andvertically by deiiecting elements 3|, 33, respectively, which deflectthe cathode ray beam across the screen II.' A control electrode 35,connected to a source of control potential, not shown, controls theelectron current comprising the cathode ray. The anode 29 is connectedto a second source of control potential, determining the velocity of theelectrons comprising the cathode ray. The screen II comprises aplurality of layers I5, I1 of different A phosphors which producecontrasting color luminescence in response to different electronvelocities, as described by reference to the system illustrated inFigure 1. It should be understood that the system for controlling thevelocity of the electrons comprising the cathode ray may be modied inany manner known in the art.

Thus the invention disclosed herein comprises an improved multicoloriluorescent screen and an improved method of and means forelectronically bombarding said screen by electrons of differentvelocities whereby distinctive color screen fluorescence is provided asa function of the electron velocity. It should be understood that thesystem described herein may be employed as a basic feature of a colortelevision system wherein color differentiation is accomplished byvarying the velocity of the scanning electron beam of the televisionreceiver kinescope.

I claim as my invention:

1. A color-selective electron microscope comprising an electron gun forgenerating an electron beam, a specimen in the path of said beam havingdifferent portions which vary differently the velocity of electronsconstituting said beam, and a pair of screens of fluorescent materialshaving different electron-fluorescent color characteristics responsiveto predetermined different irradiating electron velocities, one of saidscreens being superimposed upon the other, and means for directing saidvelocity-controlled electron beam upon said screens.

2. A color-selective cathode ray oscilloscope comprising an electron gunfor generating an electron beam, means interposed in said beam, forselectively varying the velocity of electrons in different portions ofaA cross section of said beam, and a pair of screens of fluorescentmaterials having different electron-fluorescent color characteristicsresponsive to predetermined different irradiating electron velocities,one of said screens being superimposed upon the other, the screen nearersaid gun having a lower light emission efliciency, and means fordirecting said velocity-controlled electron beam upon said screens.

3. A color-selective cathode ray oscilloscope comprising an electron gunfor generating an electron beam, means interposed in said beam, forselectively varying the velocity of electrons in different portions of across section of said beam, and a pair of screens of fluorescent ma-EDWARD G. BAMBERG.

6 REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date Rudenberg Oct. 27, 1936 VonArdenne Oct'. 26, 1937 Dawihl et a1 Oct. 31, 1939 Kaufmann Oct. 29, 1940LeVerenz May 27, 1941 Sharpe Apr. 27, 1948 Szegho Dec. 7, 1948

1. A COLOR-SELECTIVE ELECTRON MICROSCOPE COMPRISING AN ELECTRON GUN FORGENERATING AN ELECTRON BEAM, A SPECIMEN IN THE PATH OF SAID BEAM HAVINGDIFFERENT PORTIONS WHICH VARY DIFFERENTLY THE VELOCITY OF ELECTRONSCONSTITUTING SAID BEAM, AND PAIR OF SCREENS OF FLUORESCENT MATERIALSHAVING DIFFERENT ELECTRON-FLUORESCENT COLOR CHARACTERISTICS RESPONSIVETO PREDETERMINED DIFFERENT IRRADIATING ELECTRON VELOCITIES, ONE OF SAIDSCREENS BEING SUPERIMPOSED UPON THE OTHER, AND MEANS FOR DIRECTING SAIDVELOCITY-CONTROLLED ELECTRON BEAM UPON SAID SCREENS.